HIV-1 entry is triggered by interaction of the viral envelope (Env) glycoprotein gp120 with domain 1 (D1) of the T-cell receptor CD4. Ibalizumab (iMab) is a potent and broad HIV-1 neutralizing Ab (Jacobson et al., Antimicrob. Agents Chemother. 53:450-457, 2009; Kuritzkes et al., J. Infect. Dis. 189:286-291, 2004). iMab neutralizes HIV by binding mainly to domain 2 (D2) of the CD4 receptor on host T-cells, thus blocking the ability of HIV to use these CD4 receptors to gain entry into T-cells and produce infection (Burkly et al., J. Immunol. 149:1779-178, 1992). In a large panel of primary isolates (118 Env pseudotyped viruses) tested recently, iMab neutralized 92% of all viruses as defined by 50% inhibition of infection, and 47.4% of viruses as defined by 90% inhibition of infection. While iMab can potently inhibit a broad range of HIV isolates, a significant fraction of HIV variants can still escape the inhibitory activity of iMab. It has been reported recently that loss of asparagine-linked glycosylation sites in the variable region 5 of HIV type 1 envelope is associated with resistance to iMab (Toma et al., J. Virology 85(8): 3872-2880, 2011; Pace et al., J. Acquir. Immune Defic. Syndr. Epub ahead of print: September 2012).
Antibodies are glycosylated at conserved positions in their constant regions, and the presence and structure of the carbohydrate attached to the constant region can affect antibody activity (see review by Wright and Morrison, TIBTECH 15: 26-32, 1997).